Rosin acid esters are described in U.S. Pat. No. 4,775,496. These rosin acid esters are described as being particularly useful as antidegradants in polymeric compositions. As described in this patent, the rosin acid ester may be formed by reacting the rosin acid and p-hydroxydiphenylamine in the presence of toluene sulfonic acid and m-xylene. The mixture is refluxed at a pot temperature of 205.degree. C. for 24 hours. Unfortunately, this process suffers from the disadvantage of long reaction times. In addition, the upstream preparation of the p-hydroxydiphenylamine requires removal of the catalyst with isolation and purification of the p-hydroxydiphenylamine.
As mentioned above, hydroxydiphenylamine may be reacted with a rosin acid to produce an extremely useful additive for rubber Japanese Patent Application SHO 59-30388 relates to the manufacture of hydroxydiphenylamine by reacting a phenol with an aromatic amine in the presence of an ion exchanged stratified clay catalyst also known as bentonite clay.